1. Field of the Invention
The present invention relates to instruments for measuring constituents of harvested agricultural products. More particularly, though not exclusively, the present invention relates to a method and apparatus using near infrared spectrometers in combination with an agricultural implement such as a combine or chopper for real time product analysis.
2. Problems in the Art
In the field of agriculture, it is important to analyze agricultural products such as grain or forage to determine the amount of major constituents in the products. This is particularly important in breeding programs.
One prior art method of analyzing grain and other agricultural products, is using near infrared spectroscopy (NIR). NIR is a well established technique for detecting both chemical and physical properties of various materials. NIR provides an accurate and inexpensive method to analyze agricultural materials such as grain or forage. Major constituents that can be detected by using NIR include moisture, protein, oil, starch, amino acids, extractable starch, density, test weight, digestibility, cell wall content, and any other constituents or properties that are of commercial value.
There are various types of devices used for NIR. In general, these devices include light sensors in conjunction with light sources which are used with any number of measuring devices. In optical spectrometers, the incident light from a light source is passed through a monochromator, which can be a filter or set of filters, a diffraction grating, or a prism whose angular displacement relative to the incoming light can be closely correlated with the single wavelength, or narrow band of wavelengths (which it sends on to the light sensor). The light sensor is selected so that its spectral responses match the wavelength of interest. The angular motion of the prism or diffraction grating can be mechanized so that a given spectrum is scanned at a known rate over a known time interval. Such a device is referred to as a scanning spectrometer. The wavelength of an observed peak can them be determined from the time counted from the start of a scan. Spectrometers may also be referred to as spectrophotometers when their spectral range extends between ultraviolet to infrared.
The constituent content of a grain sample, for example, is measured most accurately by prior art systems by drying and grinding the sample of the grain to particulate form. The ground sample is then irradiated with near infrared light. The reflected radiation is detected at narrow band wavelengths in the NIR spectrum to obtain raw reflectance data of the sample. The data can be used to provide accurate measurements of the content of constituents of the grain samples. In many prior art systems, it is difficult to obtain accurate measurements of the grain constituents without first drying and grinding the grain into particulate form.
Other prior art systems use scanning or oscillating spectrophotometric instruments. In such an instrument, a photo detector detects light energy which is scanned through a spectrum at a rapid rate. Such an instrument employs an optical grating which receives light through an entrance slit and disperses the light into a spectrum directed toward an exit slit. The optical grating is oscillated in order to rapidly scan the light transmitted through the exist slit through the spectrum dispersed by the grating. Another prior art instrument uses filters which are tilted as they pass through a light beam to scan the transmitted light through a spectrum. Either type of instrument, the oscillating optical grating or the tilt filter type can be operated over a spectrum covering near infrared to analyze agricultural products such as grain. Using an oscillating grating or tilting filter type of instrument, the user can measure the reflectivity of the sample at narrow wavelength increments to determine the constituent contents of a grain sample. To use an oscillating grating or tilting filter instrument, the narrow bandwidth light is transmitted through the exit slit used to illuminate the grain sample. The light reflected from the sample is detected by photo detectors and the resulting photo detector signal is used to determine the constituent contents of the sample. As the grating oscillates, the center frequency of the light that irradiates the sample is swept through the NIR spectrum. Light from the diffraction grating that is reflected by the sample is detected by the photo detector. As an alternative to detecting the energy reflected from the sample, the energy may be transmitted through the sample and detected after being transmitted through the sample. In addition, instead of irradiating the sample with the output from the spectrophotometer, the sample can be irradiated with constant wideband light and a reflected light being applied to the spectrophotometer.
If a grain sample is not ground, the light absorbency and reflectance varies considerably from sample to sample. This variation is caused by light scatter from the whole grain kernels and by the nonlinear surface reflectance effects. This variation makes it difficult to obtain accurate measurements from whole grain samples. Similar problems are encountered with forage samples, especially corn forage but even more pronounced.
The spectrometers discussed require frequent calibration in order to generate accurate results. The calibrations must be performed frequently due to various dynamic factors including the change in light from a light source due to temperature sources. A typical method of calibrating (to correct for instrument response variation by baseline correction) a spectrometer is to replace the sample with a standard sample, for example, a white ceramic tile having high reflectance. The spectrometer scans the standard sample to provide standard values which are used to calibrate the spectrometer. While this calibration method works fine in a lab environment, it could be impossible, or at least impractical in the environment of an agricultural implement such as a combine or a chopper.
The spectrometers discussed above have several disadvantages. The spectrometers discussed are only suitable for use in a laboratory. Prior art methods of grain analysis have a major disadvantage resulting from the large amount of sample handling. The samples must be harvested, collected, bagged, labeled, dried, and finally sent to the NIR lab, ground and analyzed for constituent analysis. This excessive sample handling adds both cost and time to the analysis. A need can therefore be seen for an NIR instrument combined with an implement such as a combine or chopper to automate the process of collecting an analyzing grain and forage samples. Such a system would reduce the cost and time of the analysis. Such a system could provide plant breeders and grain farmers with real time information and also enhance product development through high plot screening numbers which would help develop products more rapidly.
The main problem with an NIR instrument combined with a machine such as a combine or chopper is that prior art grain or forage analysis instrumentation is very sensitive to mechanical vibrations. Scanning and oscillating spectrometers require very precise mechanical movements in order to obtain accurate results. The extreme vibrations found in the environment of a combine or chopper would result in damaged and inaccurate instrumentation equipment. In addition to the vibration, the combine or chopper environment is very dirty. The amount of dust and plant debris would severely effect the effectiveness of a conventional spectrometer.
Another problem with combining NIR instrumentation with an implement is that current NIR equipment requires a long time period for analysis. In the field of crop breeding programs, a large number of test plots are used to test products. A typical test plot of hybrid corn, for example, is comprised of two rows of corn with a length of 17 ft. A research combine used to harvest the test plots goes through each test plot in approximately 15 seconds. A typical spectrometer used in a lab to analyze grain requires more time than 10-20 seconds to analyze the grain or forage sample. Therefore, even if convention NIR instrumentation is installed on an implement, the speed of harvesting test plots would be slowed down considerably by the slow speed of the NIR instrumentation.
A need can therefore be seen for NIR equipment in combination with an implement such as a combine or chopper which could operate effectively in the environment of a combine which also is capable of analyzing product samples in a short period of time.